Hydrotreating catalyst system suitable for use in hydrotreating hydrocarbonaceous feedstreams

ABSTRACT

A stacked bed catalyst system comprising at least one first catalyst selected from conventional hydrotreating catalyst having an average pore diameter of greater than about 10 nm and at least one second catalyst comprising a bulk metal hydrotreating catalyst.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Patent ApplicationSer. No. 60/518,739 filed Nov. 10, 2003 and Ser. No. 60/608,448 filedSep. 9, 2004.

FIELD OF THE INVENTION

This invention relates to a hydrotreating catalyst system suitable foruse in hydrotreating hydrocarbonaceous feedstreams. More particularly,the present invention is directed at a stacked bed catalyst systemcomprising at least one first catalyst selected from conventionalhydrotreating catalyst having an average pore diameter of greater thanabout 10 nm and at least one second catalyst comprising a bulk metalhydrotreating catalyst.

BACKGROUND OF THE INVENTION

Environmental and regulatory initiatives are requiring ever lower levelsof both sulfur and aromatics in distillate fuels. For example, proposedsulfur limits for distillate fuels to be marketed in the European Unionfor the year 2005 is 50 wppm or less. There are also proposed limitsthat would require lower levels of total aromatics as well as lowerlevels of multi-ring aromatics found in distillate fuels and heavierhydrocarbon products. Further, the maximum allowable total aromaticslevel for CARB reference diesel and Swedish Class I diesel are 10 and 5vol. %, respectively. Further, the CARB reference fuels allows no morethan 1.4 vol. % polyaromatics (PNAs). Consequently, much work ispresently being done in the hydrotreating art because of these proposedregulations.

Still further, with the advent of increased environmental concerns, theperformance requirements for lubricating oil basestocks themselves havealso increased. For example, the American Petroleum Institute (API)requirements for Group II basestocks include a saturates content of atleast 90%, a sulfur content of 0.03 wt. % or less and a viscosity index(VI) between 80 and 120. Currently, there is a trend in the lube oilmarket to use Group II basestocks instead of Group I basestocks in orderto meet the demand for higher quality basestocks that provide forincreased fuel economy, reduced emissions, etc. For example, AmericanPetroleum Institute (API) requirements for Group II basestocks include asaturates content of at least 90%, a sulfur content of 0.03 wt. % orless and a viscosity index (VI) between 80 and 120.

Thus, as the environmental and regulatory initiatives to increase, thesearch for new and different processes, catalysts, and catalyst systemsthat exhibit improved sulfur and nitrogen removal and aromaticssaturation activity is a continuous, ongoing exercise. Therefore, thereis a need to provide hydrocarbonaceous products that meet the demand forincreased fuel economy, reduced emissions, etc.

BRIEF DESCRIPTION OF THE FIGURE

The Figure is a plot of the relative volume activity of variouscatalysts and catalyst systems versus the days the respective catalystsand catalyst systems were on stream.

SUMMARY OF THE INVENTION

The present invention is directed at a stacked bed catalyst systemsuitable for use in the hydrotreating of hydrocarbonaceous feedstocks.The catalyst system comprises:

-   -   a) at least one first catalyst selected from conventional        hydrotreating catalysts having an average pore diameter of        greater than about 10 nm; and    -   b) at least one second catalyst selected from bulk metal        hydrotreating catalysts.

DETAILED DESCRIPTION OF THE INVENTION

It should be noted that the terms “feedstock” and “feedstream” as usedherein are synonymous.

The present invention is directed at a stacked bed catalyst systemsuitable for use in the hydrotreating of hydrocarbonaceous feedstocks.The catalyst system comprises at least one first catalyst selected fromconventional hydrotreating catalysts having an average pore diameter ofgreater than about 10 nm and at least one second catalyst selected frombulk metal hydrotreating catalysts. The stacked bed hydrotreatingcatalyst system is suitable for use in the hydrotreating ofhydrocarbonaceous feedstocks.

As stated above, the present invention is a stacked bed catalyst systemcomprising at least a first and second hydrotreating catalyst. By“stacked bed” it is meant that the first catalyst appears in a separatecatalyst bed, reactor, or reaction zone, and the second hydrotreatingcatalyst appears in a separate catalyst bed, reactor, or reaction zonedownstream, in relation to the flow of the lubricating oil feedstock,from the first catalyst.

The first hydrotreating catalyst is a supported catalyst. Suitablehydrotreating catalysts for use as the first catalyst of the presentcatalyst system include any conventional hydrotreating catalyst.Conventional hydrotreating catalyst as used herein is meant to refer tothose which are comprised of at least one Group VIII metal, preferablyFe, Co and Ni, more preferably Co and/or Ni, and most preferably Ni; andat least one Group VI metal, preferably Mo and W, more preferably Mo, ona high surface area support material, preferably alumina. The Group VIIImetal is typically present in an amount ranging from about 2 to 20 wt.%, preferably from about 4 to 12%. The Group VI metal will typically bepresent in an amount ranging from about 5 to 50 wt. %, preferably fromabout 10 to 40 wt. %, and more preferably from about 20 to 30 wt. %. Allmetals weight percents are on support. By “on support” we mean that thepercents are based on the weight of the support. For example, if thesupport were to weigh 100 g. then 20 wt. % Group VIII metal would meanthat 20 g. of Group VIII metal was on the support.

However, not all conventional hydrotreating catalysts fitting theabove-described criteria are suitable for use in the present invention.The inventors hereof have unexpectedly found that the average porediameter of the first catalyst must have a specific size to be suitablefor use herein. Thus, in the practice of the present invention, aconventional catalyst, as described above, but having an average porediameter greater than 10 nm, as measured by water adsorptionporosimetry, must be used as the first catalyst of the present stackedbed catalyst system. It is preferred that the average pore diameter ofthe first catalyst, i.e. the conventional hydrotreating catalyst, of thepresent stacked bed catalyst system be greater than 11 nm, morepreferably greater than 12 nm.

The second hydrotreating catalyst is a bulk metal catalyst. By bulkmetal, it is meant that the catalysts are unsupported wherein the bulkcatalyst particles comprise 30-100 wt. % of at least one Group VIIInon-noble metal and at least one Group VIB metal, based on the totalweight of the bulk catalyst particles, calculated as metal oxides andwherein the bulk catalyst particles have a surface area of at least 10m²/g. It is furthermore preferred that the bulk metal hydrotreatingcatalysts used herein comprise about 50 to about 100 wt. %, and evenmore preferably about 70 to about 100 wt. %, of at least one Group VIIInon-noble metal and at least one Group VIB metal, based on the totalweight of the particles, calculated as metal oxides. The amount of GroupVIB and Group VIII non-noble metals can easily be determined VIBTEM-EDX.

Bulk catalyst compositions comprising one Group VIII non-noble metal andtwo Group VIB metals are preferred. It has been found that in this case,the bulk catalyst particles are sintering-resistant. Thus the activesurface area of the bulk catalyst particles is maintained during use.The molar ratio of Group VIB to Group VIII non-noble metals rangesgenerally from 10:1-1:10 and preferably from 3:1-1:3. In the case of acore-shell structured particle, these ratios of course apply to themetals contained in the shell. If more than one Group VIB metal iscontained in the bulk catalyst particles, the ratio of the differentGroup VIB metals is generally not critical. The same holds when morethan one Group VIII non-noble metal is applied. In the case wheremolybdenum and tungsten are present as Group VIB metals, themolybenum:tungsten ratio preferably lies in the range of 9:1-1:9.Preferably the Group VIII non-noble metal comprises nickel and/orcobalt. It is further preferred that the Group VIB metal comprises acombination of molybdenum and tungsten. Preferably, combinations ofnickel/molybdenum/tungsten and cobalt/molybdenum/tungsten andnickel/cobalt/molybdenum/tungsten are used. These types of precipitatesappear to be sinter-resistant. Thus, the active surface area of theprecipitate is remained during use. The metals are preferably present asoxidic compounds of the corresponding metals, or if the catalystcomposition has been sulfided, sulfidic compounds of the correspondingmetals.

It is also preferred that the bulk metal hydrotreating catalysts usedherein have a surface area of at least 50 m²/g and more preferably of atleast 100 m²/g. It is also desired that the pore size distribution ofthe bulk metal hydrotreating catalysts be approximately the same as theone of conventional hydrotreating catalysts. More in particular, thesebulk metal hydrotreating catalysts have preferably a pore volume of0.05-5 ml/g, more preferably of 0.1-4 ml/g, still more preferably of0.1-3 ml/g and most preferably 0.1-2 ml/g determined by nitrogenadsorption. Preferably, pores smaller than 1 nm are not present.Furthermore these bulk metal hydrotreating catalysts preferably have amedian diameter of at least 50 nm, more preferably at least 100 nm, andpreferably not more than 5000 μm and more preferably not more than 3000μn. Even more preferably, the median particle diameter lies in the rangeof 0.1-50 μm and most preferably in the range of 0 5-50 μm.

The reaction stage containing the stacked bed hydrotreating catalystsystem used in the present invention can be comprised of one or morefixed bed reactors or reaction zones each of which can comprise one ormore catalyst beds of the same or different catalyst. Although othertypes of catalyst beds can be used, fixed beds are preferred. Such othertypes of catalyst beds include fluidized beds, ebullating beds, slurrybeds, and moving beds. Interstage cooling or heating between reactors,reaction zones, or between catalyst beds in the same reactor, can beemployed since some olefin saturation can take place, and olefinsaturation and the desulfurization reaction are generally exothermic. Aportion of the heat generated during hydrotreating can be recovered.Where this heat recovery option is not available, conventional coolingmay be performed through cooling utilities such as cooling water or air,or through use of a hydrogen quench stream. In this manner, optimumreaction temperatures can be more easily maintained.

The stacked bed catalyst system of the present invention comprises about5-95 vol. % of the first catalyst with the second catalyst comprisingthe remainder, preferably about 40-60 vol. %, more preferably about 5 toabout 50 vol. %. Thus, if the catalyst system comprises 50 vol. % of thefirst catalyst, the second catalyst will comprise 50 vol. % also.

As stated above, the present catalyst system is suitable for use in thehydrotreating of hydrocarbonaceous feedstreams. By hydrocarbonaceousfeedstream, it is meant a primarily hydrocarbon material obtained orderived from crude petroleum oil, from tar sands, from coalliquefaction, shale oil and hydrocarbon synthesis. Thus,hydrocarbonaceous feedstreams suitable for treatment with the presentinvention include those feedstreams boiling from the naphtha boilingrange to heavy feedstocks, such as gas oils and resids, and also thosederived from Fischer-Tropsch processes. Typically, the boiling rangewill be from about 40° C. to about 1000° C. Non-limiting examples ofsuitable feedstreams include vacuum gas oils; distillates includingnaphtha, diesel, kerosene, and jet fuel; heavy gas oils, raffinates,lube oils, etc.

Hydrocarbonaceous boiling range feedstreams suitable for treatment withthe present invention include, among other things, nitrogen and sulfurcontaminants. Typically, the nitrogen content of such streams is about50 to about 1000 wppm nitrogen, preferably about 75 to about 800 wppmnitrogen, and more preferably about 100 to about 700 wppm nitrogen. Thenitrogen appears as both basic and non-basic nitrogen species.Non-limiting examples of basic nitrogen species may include quinolinesand substituted quinolines, and non-limiting examples of non-basicnitrogen species may include carbazoles and substituted carbazoles. Thesulfur content of the hydrocarbonaceous boiling range feedstream willgenerally range from about 50 wppm to about 7000 wppm, more typicallyfrom about 100 wppm to about 5000 wppm, and most typically from about100 to about 3000 wppm. The sulfur will usually be present asorganically bound sulfur. That is, as sulfur compounds such as simplealiphatic, naphthenic, and aromatic mercaptans, sulfides, di- andpolysulfides and the like. Other organically bound sulfur compoundsinclude the class of heterocyclic sulfur compounds such as thiophene,tetrahydrothiophene, benzothiophene and their higher homologs andanalogs. The hydrocarbonaceous feedstreams suitable for use herein alsocontain aromatics, which are typically present in an amount ranging fromabout 0.05 wt. %, to about 2.5 wt. %, based on the hydrocarbonaceousboiling range feedstream.

Preferred feedstocks suitable for treatment with the present inventionare wax-containing feeds that boil in the lubricating oil range,typically having a 10% distillation point greater than 650° F. (343° C.)and an endpoint greater than 800° F. (426° C.), measured by ASTM D 86 orASTM 2887. These feedstocks can be derived from mineral sources,synthetic sources, or a mixture of the two. Non-limiting examples ofsuitable lubricating oil feedstocks include those derived from sourcessuch as oils derived from solvent refining processes such as raffinates,partially solvent dewaxed oils, deasphalted oils, distillates, vacuumgas oils, coker gas oils, slack waxes, foots oils and the like, dewaxedoils, automatic transmission fluid feedstocks, and Fischer-Tropschwaxes. Automatic transmission fluid (“ATF”) feedstocks are lube oilfeedstocks having an initial boiling point between about 200° C. and275° C., and a 10% distillation point greater than about 300° C. ATFfeedstocks are typically 75-110N feedstocks.

These feedstocks may also have high contents of nitrogen- andsulfur-contaminants. Feeds containing up to 0.2 wt. % of nitrogen, basedon feed and up to 3.0 wt. % of sulfur can be processed in the presentprocess. Feeds having a high wax content typically have high viscosityindexes of up to 200 or more. Sulfur and nitrogen contents may bemeasured by standard ASTM methods D5453 and D4629, respectively.

As stated above, the present invention is suitable in hydrotreatingprocesses. It should be noted that the term “hydrotreating” as usedherein refers to processes wherein a hydrogen-containing treat gas isused in the presence of a suitable catalyst that is primarily active forthe removal of heteroatoms, such as sulfur, and nitrogen, and saturationof aromatics. If the present invention is employed in a hydrotreatingprocess, a hydrocarbonaceous feedstream is contacted with the stackedbed catalyst system in a reaction stage operated under effectivehydrotreating conditions. By effective hydrotreating conditions, it ismeant those conditions effective at removing at least a portion of thesulfur contaminants from the hydrocarbonaceous feedstream. Effectivehydrotreating conditions generally include temperatures of from 150 to400° C., a hydrogen partial pressure of from 1480 to 20786 kPa (200 to3000 psig), a space velocity of from 0.1 to 10 liquid hourly spacevelocity (LHSV), and a hydrogen to feed ratio of from 89 to 1780 m³/m³(500 to 10000 scf/B).

The contacting of the hydrocarbonaceous feedstock with the stacked bedhydrotreating catalyst system produces a hydrotreated effluentcomprising at least a gaseous product and a hydrotreatedhydrocarbonaceous feedstock. The hydrotreated effluent is stripped toremove at least a portion of the gaseous product from the hydrotreatedeffluent. The means used to strip the hydrotreated effluent can beselected from any stripping method, process, or means known can be used.Non-limiting examples of suitable stripping methods, means, andprocesses include flash drums, fractionators, knock-out drums, steamstripping, etc.

The above description is directed to preferred embodiments of thepresent invention. Those skilled in the art will recognize that otherembodiments that are equally effective could be devised for carrying outthe spirit of this invention.

The following examples will illustrate the improved effectiveness of thepresent invention, but is not meant to limit the present invention inany fashion.

EXAMPLES Example 1

A medium vacuum gas oil having the properties outlined in Table 1 wasprocessed in an isothermal pilot plant over three catalysts systems at1200 psig hydrogen partial pressure. The catalyst systems and operatingconditions are given in Table 2. Catalyst B is a conventionalhydrotreating catalyst having about 4.5 wt. % Group VI metal, about 23wt. % Group VIII metal on an alumina support and has an average poresize of 14.0 nm. The bulk metal hydrotreating catalyst was a commercialbulk metal hydrotreating catalyst marketed under the name Nebula byAkzo-Nobel.

In the Examples, all the catalyst systems were lined out at about 50days on stream. A first order kinetic model with an activation energy of31,000 cal/gmol was used to compare volume activities between thecatalysts. TABLE 1 Medium Vacuum Gas Oil Density at 70° C. (g/cc) 0.88Nitrogen (wppm) 700 Sulfur (wt. %) 2.6 GCD 5 WT % Boiling Point (° C.)334 GCD 50 WT % Boiling Point (° C.) 441 GCD 95 WT % Boiling Point (°C.) 531

TABLE 2 50 vol. % Catalyst B 100 vol. % 100 vol. % followed by CatalystSystem Catalyst B Nebula 1 50 vol. % Nebula 1 Average Catalyst 370 380370 Temperature (° C.) Liquid Hourly Space 2 1 1 Velocity (hr⁻¹)Stripped reactor 227 17 34 Effluent Nitrogen Content (wppm) NitrogenRemoval 1 1.18 1.34 Relative Volume Activity

The Nitrogen Removal Relative Volume Activity (“RVA”) for each catalystsystem was calculated by simple first order kinetic modeling. As shownin Table 2, the 50/50 vol. % stacked bed catalyst system, with the largeaverage pore size Catalyst B upstream of the bulk metal catalyst, showedhigher nitrogen removal activity than either of the single catalystsystems demonstrated on their own.

Example 2

The hydrotreating ability of different stacked beds of Catalyst B andNebula were analyzed by hydrotreating different feedstreams over thestacked beds in the in two parallel reactor trains of the sameisothermal pilot plant unit used in Example 1 above. The feedstreamsused were Medium Cycle Oils (“MCO”) from an FCC unit and blends of theMCO with a virgin feedstock were tested in two parallel reactor trains.The feed properties are described in Table 3, below.

In this Example, one reactor train consisted entirely of a conventionalNiMo on Alumina hydrotreating catalyst, Catalyst C, with an average porediameter of 7.5 nm. The other reactor train contained a stacked bedsystem with 75-vol. % of Catalyst C followed by 25-vol. % of Catalyst A,a bulk multimetallic sulfide catalyst having an average pore diameter of5.5 nm.

The separate reactors in both trains were immersed in a fluidizedsandbath for efficient heat transfer. Thus, the temperature of the first75-vol. % of Catalyst C was at the same temperature whether it was intrain 1 or 2. Likewise, the last 25-vol. % of Catalyst C in train 1 wasat the same temperature as the last 25-vol. % of Catalyst A in train 2.Therefore, In Example 2, each of the two reactor trains was divided intotwo separate reactor vessels where the temperature of the first75-volume % containing 75 vol. % of the catalyst loading of that reactorcould be independently controlled from the last 25-volume % of catalyst.

The operating conditions for the two trains were 1350 psig H₂, liquidhourly space velocities (“LHSV”) of 1.4 vol./hr/vol., and 5500-6300SCF/B of hydrogen. The temperature schedule for both trains is describedin Table 4 below. TABLE 3 FEED 50% 67% 100% 100% Normal Normal NormalHeavy FCC FCC FCC FCC MCO MCO MCO MCO API Gravity 18.1 15.0 9.5 7.0Hydrogen, wt. % 10.65 10.04 8.77 8.61 Sulfur, wt. % 3.23 3.53 4.28 4.40Nitrogen, ppm 959 1153 1485 1573 Aromatics-Mono, wt. % — — 12.0 8.8Aromatics-Di, wt. % — — 43.9 41.7 Aromatics-Poly, wt. % — — 22.4 30.7Distillation, D2887 GCD 10 498 493 485 493 50 627 625 618 642 90 703 705706 749 95 726 721 724 777

TABLE 4 Days on Oil Feedstock 75%/25% Temperatures, ° F. 4-6  50% FCCMCO 585/650  7-15  67% FCC MCO 585/650 16-30 100% FCC MCO585-610/650-675 31-50 100% Heavy FCC MCO 610-635/675-700

The relative HDN volume activity of the stacked bed Catalyst C/CatalystA compared to Catalyst A is shown in the figure below. Note that for the50%, 67% and 100% FCC MCO feeds the stacked bed system with only25-volume % of Catalyst A shows a stable activity advantage of about275%.

As shown in the Figure, when the 100% Heavy FCC MCO was used as the feednote the activity advantage for the stacked bed catalyst systemcontaining begins to decrease from about 275% to about 225% and then wassubsequently reduced over about 20 days to slightly less than 150%.

Example 3

In this Example, a stacked bed catalyst system containing 75 vol. % ofCatalyst B and 25 vol. % Nebula, both as described above, was used tohydrotreat a light cycle cat oil feed (“Feed A”) and a heavier mediumcycle cat oil feed (“Feed B”) as described in Table 5 below. Example 2was conducted in the same two reactor train pilot plant unit asdescribed in Example 2 above. The operating conditions for the twotrains were 1200 psig H₂, liquid hourly space velocities of 2vol./hr/vol., and 5000 SCF/B of hydrogen.

The reactor effluents were stripped with nitrogen in an oven at 100° C.to remove substantially all of the gaseous reaction products. Thenitrogen content of the liquid reactor effluent was then analyzed byASTM 4629. The temperature schedules for both trains along with theresults of this example are described in Table 5 below. TABLE 5 FEEDFeed A Feed B API Gravity 0.973 0.9 Sulfur, wt. % 2.6 2.50 Nitrogen, ppm713 742 Distillation, D2887 GCD  5 427 448 50 551 590 95 707 755 EP 764823 Catalyst B Temperature 570 617 Nebula Temperature 645 692 StrippedReactor Effluent 2 7 Nitrogen Content Nitrogen Removal Relative 1.751.75 Volume Activity

As can be seen in Table 5, when a conventional catalyst having anaverage pore diameter of 14 nm was used in the first 75 vol. % of thereactor, the Nitrogen Removal Relative Volume Activity (“RVA”) for thecatalyst system remained constant when the heavier feed was used. Incomparing the results of Example 3 to those obtained in Example 2, onecan see that when a catalyst having a pore volume of 7.5 nm preceded thebulk metal catalyst, the RVA of the catalyst system decreased. However,in Example 3, the heavier feed did not negatively impact the RVA of thecatalyst system.

1. A stacked bed catalyst system comprising: a) at least one firstcatalyst selected from conventional hydrotreating catalysts having anaverage pore diameter of greater than about 10 nm; and b) at least onesecond catalyst selected from bulk metal hydrotreating catalysts.
 2. Thestacked bed catalyst system according to claim 1 wherein said firsthydrotreating catalyst is selected from supported hydrotreatingcatalysts comprising about 2 to 20 wt. % of at least one Group VIIImetal, and about 5 to 50 wt. % of at least one Group VI metal on a highsurface area support material having an average pore diameter of greaterthan 10 nm.
 3. The stacked bed catalyst system according to claim 2wherein said Group VIII metal is selected from Co Ni, and mixturesthereof, said Group VI metal is selected from Mo, W, and mixturesthereof, and said high surface area support material is selected fromsilica, alumina, and mixtures thereof.
 4. The stacked bed catalystsystem according to claim 1 wherein said second catalyst is a bulk metalhydrotreating catalyst comprising about 30 to about 100 wt. % of atleast one Group VIII non-noble metal and at least one Group VIB metal,based on the total weight of the bulk catalyst particles, calculated asmetal oxides and wherein the bulk catalyst particles have a surface areaof at least 10 m²/g.
 5. The stacked bed catalyst system according toclaim 4 wherein said bulk metal hydrotreating catalyst comprises oneGroup VIII non-noble metal and two Group VIB metals wherein the molarratio of Group VIB to Group VIII non-noble metals ranges from 10:1-1:10.6. The stacked bed catalyst system according to claim 5 wherein the atleast one Group VIII non-noble metal and at least one Group VIB metalsare present as oxidic compounds of the corresponding metals, or if thecatalyst composition has been sulfided, sulfidic compounds of thecorresponding metals.
 7. The stacked bed catalyst system according toclaim 1 wherein the bulk metal hydrotreating catalysts have a surfacearea of at least 50 m²/g, a pore size volume of about 0.05 to about 5ml/g, and a median diameter of at least 50 nm.
 8. The stacked bedcatalyst system according to claim 1 wherein the catalyst system of thepresent invention comprises about 5-95 vol. % of the first hydrotreatingcatalyst with the second hydrotreating catalyst comprising theremainder.
 9. The stacked bed catalyst system according to claim 1wherein said first hydrotreating catalyst has an average pore diameterof greater than 11 nm.
 10. The stacked bed catalyst system according toclaim 1 wherein said first hydrotreating catalyst has an average porediameter of greater than 12 nm.
 11. The stacked bed catalyst systemaccording to claim 1 wherein the catalyst system of the presentinvention comprises about 40-60 vol. % of the first catalyst with thesecond hydrotreating catalyst comprising the remainder.
 12. The stackedbed catalyst system according to claim 1 wherein the catalyst system ofthe present invention comprises about 5-50 vol. % of the first catalystwith the second hydrotreating catalyst comprising the remainder.